1. Field of the Invention
The present invention relates to an encoding/ decoding device for image data, adapted for use in a facsimile apparatus, an electronic file or the like.
2. Related Background Art
Compression encoding of image data is already employed in the facsimile apparatus, electronic files and the like, for improving the efficiency of transmission or storage.
FIGS. 10 and 11 illustrate examples of an encoding/decoding device.
Referring to FIG. 10, image data from an image reading unit 21 are stored in an image RAM 22 through an image bus, under the control of an image control unit 24. Subsequently, the image data from the image RAM 22 are supplied, through the image bus under DMA control, to an encoding/decoding unit 25 and all encoded therein. The code data obtained by the encoding are supplied through a system bus, under the control of a system control unit 26, to a transmission unit or a memory unit.
On the other hand, code data from a reception unit or the memory unit are supplied through the system bus to the encoding/decoding unit 25 and are decoded therein, and the decoded image data are stored in the image RAM 22, through the image bus and under the DMA control. Subsequently the image data in said image RAM 22 are supplied through the image bus to a printer unit 23 and are reproduced on a recording material such as paper.
In the structure shown in FIG. 11, image data from a reading unit 31 are stored in an image RAM 35 through a system bus, under the control of an image control unit 34. Subsequently, the image data from the image RAM 35 are supplied through a system bus to an encoding/decoding unit 32 and are encoded therein. The code data obtained by said encoding are supplied to a transmission unit or a memory unit through a system bus, under the control of a system control unit 34.
On the other hand, code data from a reception unit or the memory unit are supplied through the system bus to the encoding/decoding unit 32 and are decoded therein, and the decoded image data are stored in the image RAM 35 through the system bus. Subsequently the image data in said image RAM 35 are supplied through the system bus to a printer unit 33 and are reproduced on a recording material such as paper.
However, the structure shown in FIG. 10 is associated with the drawback of repairing large-sized circuitry, since it requires two data buses, namely the system bus and the image bus, and also a control unit 26 for the system bus and a control unit 24 for the image bus.
Also, the encoding/decoding unit 26 cannot execute the encoding and the decoding at the same time. Consequently, in a facsimile apparatus designed to transmit encoded data stored in advance in a large-capacity memory attached to the system bus, there is required a long processing time for obtaining data for transmission, since the code data in said memory are decoded to reproduce the original image in the memory of the image bus and are again subjected to an encoding process suitable for transmission.
Also there is required a long access time, since the image RAM 22 for exchanging the image data with the encoding/decoding unit 25 is composed of an external memory.
On the other hand, the structure shown in FIG. 11 does not require separate system and image buses.
However, the processing ability of the system control unit 34 is significantly deteriorated, because the input and output of the image data and the code data to and from the encoding/decoding unit 32, the transmission of data from the reading unit 31 to the image RAM 35, and that from the image RAM 35 to the printer unit 33 are all conducted through the system bus.